Absolutely. I decided to stop making the effort and my ds's cousins commented about what a long time it had been since they saw him when we did finally see them. Yes funny that.
After a particularly miserable visit to the zoo when my oldestr nephew's behaviour was so dire and rude (and actually drove me to tears) I said I'd have no more of it. Why was I doing that to myself simply so ds could have a elationship with his cousins when my sister clearly wasn't bothered.
So I was totally fed up of doing all the running, issuing all the invites and never getting any invites or offers in return and people never coming to my house.
I relented for a while (ds is an only child and always asking for company at weekends etc). But this simply led to a big row with my sister and I haven't spoken to her since.
And actually I feel so much better with all that expectation, miserableness at my family's complete lack of effort etc lifted from my shoulders. I no longer stress or worry about why and what I can do to make sure he sees his cousins, and don't feel put upon by being the one bending over backwards to help my sister all the time.
I don't see my family at all now apart from my parents occassionally (but again I still have to drag myself over to theirs). I usually send ds up there on his own now to be honest, he's old enough to walk the 2 minutes to theirs now.
Cutting myself off and stopping the running around and favours for them with nothing in return has been the best thing I did. Ds gets sad sometimes he doesn't see his cousins. But like I said to him we only saw them when we made the effort and it's better to have friends over who invite him back too. And he was getting a bit fed up with my oldest nephew's behaviour too which has helped a little in dealing with the not seeing them.
It is tough, but you need to do what is best for you. And perhaps distancing yourself from them a little will help clarify for you whether they realise and care enough to make some effort, or whether they're just not that bothered, in which case why keep trying.